1. Field of the Invention
The invention relates to a wear coating for a magnetic head and more particularly to a single thin film silicon based wear coating which is comparable to multi-layer thin film wear coatings.
2. Description of the Related Art
A magnetic head is employed in a disk drive for reading and writing information in tracks on the surface of a rotating disk. The magnetic head is provided in (or, on) a slider which is, in turn, mounted on a suspension. The suspension is mounted on an actuator which positions the magnetic head at tracks on the magnetic disk. As the disk rotates, an air cushion is generated between the rotating disk and an air bearing surface (ABS) of the slider. A loading force of the suspension counterbalances the force of the air cushion, causing the magnetic head to be spaced a slight distance from the surface of the disk, on the order of 0.075 .mu.m, as the disk rotates. The smaller the spacing, the greater the areal density achievable with the magnetic head. Areal density is the number of bits that the magnetic head can read per square inch of the disk's surface.
Manifestly, head-to-disk spacing imposes a limit on areal density for any particular head. The difference between the areal density that would be theoretically achievable if the head contacted the disk surface and the areal density achievable at any head-to-disk spacing represents a loss in data storage capability that is referred to as "spacing loss". Of course, a head which makes contact with the surface of the disk has no spacing loss. Such contact, however, would result in unacceptable wear of the head.
Spacing loss is also caused by a wear coating which may be applied to the ABS of a head to protect sensitive elements of the head. For example, a combined head may include an inductive write head portion and an MR read head portion. The sensitive element of the write head portion includes a pair of pole tips which are separated by a gap, and the sensitive element of a read head portion includes an MR sensor. During take off and landing of the slider, contact with the disk surface can abrade the sensitive elements of a combined magnetic head. Wear of the sensitive elements shortens them, causing degradation of head performance. Accordingly, an art has developed which provides wear coatings for magnetic heads. A strong felt need in this art is to keep the wear coating as thin as possible so as to minimize spacing loss.
In commonly assigned U.S. Pat. No. 5,175,658 tri-layer wear coating is described. The first layer, which covers the rails of a slider and the sensitive element of a magnetic head mounted thereon, is a 10-50 .ANG. thick adhesion layer of silicon. The next layer is a 50-1000 .ANG. thick layer of amorphous hydrogenated carbon. The final layer, which forms the ABS of the slider, is a 50 .ANG. thick layer of silicon. An alternative protective coatmg employed by the assignee comprises two layers: a 10 .ANG. thick adhesion layer of silicon and a final 35 .ANG. thick layer of amorphous hydrogenated carbon.
Formation of these wear coatings requires a sputtering step for each layer. Thus, the three-layer coating of the '658 patent requires three sputtering steps, while the two-layer coating requires two. It can well be appreciated that each sputtering step incrementally increases the cost of manufacturing. It would be desirable if the wear coating could be applied in one sputtering step. U.S. Pat. No. 5,323,283 employs a single layer wear coating which is applied in one sputtering step. The single layer wear coating is a 175-225 .ANG. thick layer of silicon dioxide. It would be desirable if the thicknesses of this single layer could be reduced as far as possible so as to minimize spacing loss. Accordingly, there is a strong felt need for a single layer wear coating which provides an ideal minimum spacing loss over state of the art wear coatings.